Pair-rule patterning in the honeybee Apis mellifera: Expression of even-skipped combines traits known from beetles and fruitfly.

We have studied the binding pattern of antibody mAB 2B8 directed against even-skipped orthologous proteins (EVE) in honeybee embryos. Primary and secondary EVE stripes form in roughly anterior-to-posterior succession; there are 8 primary and 16 secondary stripes. The most posterior primary stripes appear only after the onset of gastrulation. The secondary stripes form by a splitting of primary stripes; they demarcate the parasegmental pattern. While these findings resemble EVE expression in long-germ beetles, the honeybee differs from both beetles and dipterans by two transient pair-rule traits in the parasegmental EVE pattern: the secondary stripes in head and thorax alternate in strength, yet out of register with the Drosophila pattern, and over the whole pattern the odd-numbered stripes vanish earlier than their even-numbered counterparts. As in Drosophila, however, the strong EVE stripes coincide with the weak engrailed (EN) stripes. These findings are taken to indicate that (1) honeybee and beetles share a conserved mode of EVE stripe formation whilst Drosophila has diverged in this respect, (2) honeybee and Drosophila have diverged from the beetles in specific pair-rule traits during the parasegmental expression of both EVE and EN, and (3) some of these traits differ in the register of segment pairing and thus may reflect regulatory divergences at the pair-rule level between dipterans and the honeybee.